The long-term objectives are to study differences in regional cerebral metabolic rates between depressed patients and normal controls before and after sleep deprivation (SD) to develop a better understanding of sleep and the pathophysiology of depression. Cerebral metabolic rates will be assessed with positron emission tomography (PET), using 18 F- fluorodeoxyglucose (FDG). First, we hope to replicate our previous finding of a decreased ratio of caudate/whole slice metabolic rates (C/WS-MR) in bipolar and unipolar depressed subjects compared to normal subjects. This may be useful as a potential diagnostic marker for depression. Second, we propose studying the relationship between the C/WS-MR and change in mood induced by SD. In a recent review of 55 studies with over 1,500 depressed patients, SD was found to be a rapid, nonpharmacologic, but temporarily efficacious antidepressant intervention for one to two-thirds of depressed patients. In previous studies, other types of antidepressant induced euthymia resulted in normalization of decreased C/WS-MR in depressed subjects. We hypothesize that the C/WS-MR will be increased in depressed patients relative to normal controls after sleep deprivation with the degree of change positively correlated with clinical improvement in mood. We hypothesize that depressed subjects with the lowest caudate metabolism will have the greatest antidepressant response to SD. Other parameters such as global metabolism, hemispheric differences, and anteroposterior differences will also be assessed. Twenty-four patients with a major depressive episode, twelve normal, and twelve anxious but not depressed controls will be studied with PET scan, using FDG before and after sleep deprivation (SD).